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Here's a useful mnemonic rhyme for the international "rule of the road" used for the right of way when any two ships are converging:

If, to your STARBOARD, RED appear
It is your duty to keep clear;
To act as judgement says is proper,
To starboard - or port - back - or stop her.

But when, upon your PORT, is seen
A steamer's starboard light of GREEN,
There's not so much for you to do,
For Green to Port keeps clear of you.

A separate page contains mnemonics for port and starboard lights and ways to remember port and starboard.

Three further short rhymes provide a good summary of how to respond to vessels carrying navigation lights, especially when they are head-to-head:

If to your starboard Red appear
It is your duty to keep clear.

Green to Green or Red to Red
In perfect safety go ahead.

But when both lights you see ahead
"Port your helm" (or starboard your wheel)
And show your Red.

The phrase "port your helm" refers to the use of a tiller. In helm orders, one has to recall that all ships were once steered by a tiller (or lever arrangement). If one puts the tiller over to port (ie.left), the rudder and consequently the ship's head went round to starboard (ie.right). Therefore the helm order "port" meant that the ship was to turn to starboard. Much later, after steam and steam steering became almost universal, helm orders were changed by international agreement, whereby "port" meant only "turn to port".